全文获取类型
收费全文 | 1251篇 |
免费 | 124篇 |
国内免费 | 127篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 108篇 |
地球物理 | 148篇 |
地质学 | 418篇 |
海洋学 | 39篇 |
天文学 | 337篇 |
综合类 | 49篇 |
自然地理 | 370篇 |
出版年
2024年 | 3篇 |
2023年 | 9篇 |
2022年 | 33篇 |
2021年 | 30篇 |
2020年 | 30篇 |
2019年 | 41篇 |
2018年 | 37篇 |
2017年 | 36篇 |
2016年 | 46篇 |
2015年 | 55篇 |
2014年 | 50篇 |
2013年 | 78篇 |
2012年 | 42篇 |
2011年 | 57篇 |
2010年 | 45篇 |
2009年 | 84篇 |
2008年 | 66篇 |
2007年 | 81篇 |
2006年 | 84篇 |
2005年 | 84篇 |
2004年 | 75篇 |
2003年 | 59篇 |
2002年 | 64篇 |
2001年 | 55篇 |
2000年 | 39篇 |
1999年 | 42篇 |
1998年 | 35篇 |
1997年 | 16篇 |
1996年 | 20篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有1502条查询结果,搜索用时 296 毫秒
121.
R.J.R. Williams D. Ward-Thompson A.P. Whitworth 《Monthly notices of the Royal Astronomical Society》2001,327(3):788-798
We present hydrodynamical simulations of the formation, structure and evolution of photoionized columns, with parameters based on those observed in the Eagle Nebula. On the basis of these simulations we argue that there is no unequivocal evidence that the dense neutral clumps at heads of the columns were cores in the pre-existing molecular cloud. In our simulations, a variety of initial conditions leads to the formation and maintenance of near-equilibrium columns. Therefore, it is likely that narrow columns will often occur in regions with large-scale inhomogeneities, but that observations of such columns can tell us little about the processes by which they formed. The manner in which the columns in our simulations develop suggests that their evolution may result in extended sequences of radiation-induced star formation. 相似文献
122.
Guillermo Bosch † Elena Terlevich ‡ Roberto Terlevich § 《Monthly notices of the Royal Astronomical Society》2002,329(3):481-496
We have obtained accurate CCD narrow-band Hβ and Hα photometry of giant H ii regions (GEHRs) in M33, NGC 6822 and M101. Comparison with previous determinations of emission-line fluxes shows large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion ( σ ) derived from emission linewidths, we review the relation. A re-analysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we find that a subsample – which we refer to as young and single GEHRs – do follow a tight relation in the plane. 相似文献
123.
太阳第21周实测到3986个活动区,以黑子面积、X射线耀斑指数、10.7cm射电爆发及质子事件等四项指数,从中综合评估出AR3804、AR4474等16个最强烈活动区。与22周比较,两周都有在时空分布的相对集中性特征。但21周集中在4个时段,不如22周在2个时段集中;21周出现的5个热点,只有南半球在经度85°前后的热点,与22周3个热点之一相似;21周的整体活动水平略低,在X射线和质子事件两方面尤为显著低于22周 相似文献
124.
为研究柴北缘东部及周缘侏罗系发育特征及其对构造活动的响应,笔者等基于柴北缘东段红山、霍布逊及德令哈凹陷侏罗系野外地质调查,通过地层接触关系追踪、二维地震资料解释以及岩性岩相突变特征分析,同时与中国西北地区其他典型的盆地侏罗系发育特征进行对比分析,研究表明,在中国西北多个板块的相互作用的构造背景之下,柴北缘东段燕山期构造运动Ⅰ幕发生在早—中侏罗世,以古地理与古构造环境较为均一、发育粗碎屑凹陷、每个凹陷内具有幕式沉积充填特征,与中国西北其他盆地对比,此幕构造运动波及面大,但强度较弱,推测与中国西北周边各板块碰撞造山之后的伸展作用相关;燕山期构造运动Ⅱ幕发生在晚侏罗世—早白垩世,此幕构造运动导致古地理与古构造环境向新的环境转变,以中—上侏罗统之间的角度不整合、白垩系及晚侏罗统的残缺不全为特征,推测与拉萨地块与欧亚板块碰撞以及蒙古—鄂霍茨克洋的关闭及Kolyma—Omolon地块的碰撞有关。 相似文献
125.
126.
C. R. Purcell R. Balasubramanyam M. G. Burton A. J. Walsh V. Minier M. R. Hunt-Cunningham L. L. Kedziora-Chudczer S. N. Longmore T. Hill I. Bains P. J. Barnes A. L. Busfield P. Calisse N. H. M. Crighton S. J. Curran T. M. Davis J. T. Dempsey G. Derragopian B. Fulton M. G. Hidas M. G. Hoare J.-K. Lee E. F. Ladd S. L. Lumsden T. J. T. Moore M. T. Murphy R. D. Oudmaijer M. B. Pracy J. Rathborne S. Robertson A. S. B. Schultz J. Shobbrook P. A. Sparks J. Storey T. Travouillion 《Monthly notices of the Royal Astronomical Society》2006,367(2):553-576
127.
Jim Cohen 《Astrophysics and Space Science》2005,295(1-2):27-36
Magnetic field strengths and directions can be estimated using many different observational techniques that span a wide range of wavelengths. Each observational method favours different regimes of scale size, density and other physical conditions. The available techniques and their ranges of applicability are briefly described and the current status of observations is reviewed, with particular emphasis on high-resolution observations of star-forming regions. 相似文献
128.
Kirsty J. Rhook Martin G. Haehnelt 《Monthly notices of the Royal Astronomical Society》2006,373(2):623-631
H ii regions surrounding supermassive black holes (SMBHs) in an otherwise still neutral intergalactic medium (IGM) are likely to be the most easily detectable sources by future 21-cm experiments like LOFAR. We have made predictions for the size distribution of such H ii regions for several physically motivated models for BH growth at high redshift and compared this to the expected LOFAR sensitivity to these sources. The number of potentially detectable H ii regions does not only depend on the ionization state of the IGM and the decoupling of the spin temperature of the neutral hydrogen from the cosmic microwave background temperature, but is also strongly sensitive to the rate of growth of BHs at high redshift. If the SMBHs at redshift 6 were built up via continuous Eddington-limited accretion from low mass seed BHs at high redshift, then LOFAR is not expected to detect isolated QSO H ii regions at redshifts much larger than 6, and only if the IGM is still significantly neutral. If the high-redshift growth of BHs starts with massive seed BHs and is driven by short-lived accretion events following the merging of BH hosting galaxies then the detection of H ii regions surrounding SMBHs may extend to redshifts as large as 8–9 but is still very sensitive to the redshift to which the IGM remains significantly neutral. The most optimistic predictions are for a model where the SMBHs at z > 6 have grown slowly. H ii regions around SMBHs may then be detected to significantly larger redshifts. 相似文献
129.
河南省电子政务空间信息服务系统建设与典型应用 总被引:2,自引:0,他引:2
介绍了河南省电子政务空间信息服务系统的项目背景、系统总体设计,论述了数据处理与集成建库所涉及的一些关键技术,并以中原城市群空间信息服务系统为典型应用,作了进一步的探讨。 相似文献
130.